Investigation on the properties of pure and doped nanocrystalline ZnO films

Abstract

The physical properties of pure and doped zinc oxide (ZnO) films grown by sol-gel spin coating technique are studied in detail. The optimizations of annealing temperature and number of layers of undoped ZnO film growth are initially undertaken. Structural properties are characterized by XRD, FESEM and EDAX or XPS. Optical properties through UV-Vis-NIR, Photoluminescence and Magnetic properties by vibrating sample magnetometer are studied. The XRD patterns show that ZnO films are polycrystalline in nature and crystallite size varies from 10 to 46 nm. Lattice constants a and c are calculated and they are in good agreement with the standard result. SEM images of pure and doped ZnO are well defined and depict the hexagonal structure. The grain size of the ZnO nanoparticles decreases with doping. The chemical compositions of all the ZnO nanocrystalline films are determined by the typical EDAX and XPS. Quantitative analysis was carried out using the XPS to find the stoichiometry of ZnO films. Observation of Zn 2p3/2 and O 1s peaks confirm the presence of these elements in the ZnO film studied here. The absorption coefficient and energy band-gap are determined from the UV-Vis transmission measurement. The band-gap of manganese doped zinc oxide is observed with largest deviation from pure ZnO which varies from 2.55 to 2.72 eV. Photoluminescence measurements are used to evaluate the optical and crystalline quality of the undoped and doped ZnO thin films. Strong near band edge (NBE) emission dominates for all samples in the PL spectra taken at room temperature. Undoped and Al, Cd, Ce and Er doped ZnO shows NBE around 383 nm but TM (Mn, Co, Ni) doped ZnO films exhibit NBE around 415 nm. The bare and doped ZnO films prepared are examined for magnetization studies at room temperature in the range of the magnetic field 0 17.5 kOe. Non ferromagnetism for pure and ferromagnetism for doped ZnO films are observed.